Studies on the cerebral circulation of the baboon in acutely induced hypertension.

The upper limit autoregulation of cerebral blood flow was investigated in eight young baboons with the intracarotid 133xenon clearance method. Blood pressure was increased by intravenous angiotensin infusion. Autoregulation was effective during blood pressure increase from normotensive levels to a mean pressure of 130 to 139 mm Hg. At this pressure, cerebrovascular resistance reached a maximum. With further blood pressure increase, autoregulation was broken, and the vascular resistance dropped significantly. This flow increase was restricted to the fast component of the 133xenon clearance curve, leaving slow component unchanged.